1. Field of the Invention
The present invention relates to a fluid valve control system adapted to control the flow of fluid to a device such as a hydraulic actuator, spool valve, or servomotor.
2. Background Information
Hydraulic control valve systems can be used to control hydraulically driven actuators. For example, earthmoving, material handling, construction, agricultural, or industrial equipment, or the like, may contain one or more hydraulically driven piston type actuators which move a bucket, dozer blade, shovel, forklift, boom, plow, planter, harvester etc. The hydraulic control valve system may control the flow of fluid to and from the actuator to induce a corresponding movement of the actuator piston.
U.S. Pat. No. 4,870,892 issued to Thomsen et al. on Oct. 3, 1989 discloses a hydraulic control valve system that can control the flow of fluid to a device such as an actuator. The control valve system includes a spool valve or servomotor that contains an internal spool. The spool can move within a valve housing to control the flow of fluid to the actuator. One end of the spool is coupled to a first fluid chamber. The other end of the spool is coupled to a second fluid chamber. Providing a pressurized fluid to the first fluid chamber moves the spool in a first direction. Pressurizing the second fluid chamber moves the spool in an opposite second direction. The spool can be moved into a neutral position by a pair of springs when both fluid chambers are connected to a drain line.
The Thomsen et al. control valve system has a pair of supply or pilot control valves that can be actuated to couple the fluid chambers of the spool valve to a pressurized supply line. The actuator valve also has a pair of drain control valves that can be actuated to couple the fluid chambers to the drain line. The supply control valves are normally closed. The drain control valves are normally open.
The control valves are connected to an electronic controller that controls the operation of the spool by providing a series of electrical pulses to the control valves. By way of example, the controller can provide current to open the supply control valve and close the drain control valve of the first fluid chamber. In this state the first chamber is pressurized to move the spool.
The control valves disclosed in Thomsen et al. are analog valves that can only move to the open or closed positions in response to an electrical current from the controller. The valves will return to a neutral state, either open or closed, upon the termination of the current. The analog valves thus require a continuous supply of current to switch from the natural state. The continuous current supply consumes power and may introduce undesirable heat within the valves. The heat may reduce the life of the valves. It would be desirable to provide a hydraulic control valve system which does not consume as much power or produce as much heat as control valve systems of the prior art.
The controller may receive an input command from an input device such as a joystick. The controller translates the input command to a desired spool position. The control valve system may have a sensor that detects the position of the spool and provides a position signal to the controller. The controller may compute an error value which corresponds to the difference between the desired position and the actual position. The controller may then provide electrical power to the control valves to move the spool toward the desired position based on the error value.
The controller may continuously calculate an error value and then provide power to the control valves to adjust the spool position in accordance with a servo routine. Actuating the control valves each time there is an error may not be an efficient use of power particularly if the error is a relatively small value. The continuous actuation of the control valves must be balanced with the desired accuracy of the spool position. It would be desirable to provide a control system for a hydraulic control valve system that optimizes electrical power consumption while minimizing tracking error.